Hard disk drives have become much bigger, and it is common to use a 2TB or 4TB single disk. Since many servers are built with hardware RAID arrays, the virtual disk may be larger than 10TB. If you build a RAID 5 array with three 3TB hard disks, the virtual disk in Disk Management is 6TB. If this disk is initialized as MBR, you can only use 2TB of space; the remaining 4TB of disk space is shown as "Unallocated" at the end. This space cannot be used to create new volumes or expand other partitions. To use the full disk space, you must convert the disk from MBR to GPT. If there are 4 partitions on a disk and Windows does not allow creating more volumes, you also need to change the MBR disk to GPT. This article introduces how to convert MBR to GPT in Windows Server 2012 R2 with the MBR2GPT command tool and disk conversion software.
Convert MBR to GPT in Server 2012 R2 via Disk Management (Destructive)
To convert an MBR disk to GPT in Windows Server 2012 R2, there are several ways. Windows has built-in Disk Management and the diskpart command tool to help convert the disk type, but you must delete all partitions on this MBR disk in advance.
In the diskpart command prompt window, type help convert GPT, and you will see the syntax, note, and example of the convert command.
In the Disk Management console, when you right-click the leftmost area of an MBR disk, there is also an option, but "Convert to GPT Disk" is grayed out if there is a partition on it.
With MBR2GPT.exe (provided by Microsoft) and NIUBI Partition Editor, you can convert MBR to GPT in Server 2012 R2 without losing data. Before starting, make sure the MBR disk that you want to convert is a data disk or a system disk, because the method is different.
How to Convert MBR to GPT for a Non-System Disk
If there is only data on the MBR disk, it is extremely easy and fast to convert it to GPT without losing data; only several clicks are needed.
Steps to convert MBR to GPT in Server 2012 R2 without losing data:
- Download NIUBI Partition Editor, right-click the leftmost area of this MBR disk, and select "Convert to GPT Disk".
- Simply click "Yes" to confirm, then a pending operation is added.
- Click Apply on the top left to execute, and you are done. (All operations before clicking "Apply" only work in virtual mode.)
Watch the video to see how to convert a disk from MBR to GPT in Windows Server 2012:
How to Convert MBR to GPT in Windows Server 2012 for a System Disk
If there is an operating system on the MBR disk, it is a bit complicated, because all system files must remain intact and the OS must boot correctly after converting to GPT. There is some third-party software that claims to be able to convert an MBR disk to GPT with an operating system on it, but few can ensure that the system is 100% bootable. If you want to convert the system disk from MBR to GPT in Server 2012 R2, it is suggested to run MBR2GPT.exe, which is a command prompt tool provided by Microsoft.
Server 2012 MBR2GPT.exe Command Prompt
MBR2GPT.exe runs from the command prompt. On Windows Server 2019 and Windows 10 (1703 and later versions), you can convert MBR to GPT with this command in Windows. But to run MBR2GPT in Server 2012 R2, you need bootable media with the Windows Preinstallation Environment (Windows PE).
To convert MBR to GPT on a Windows 2012 server with the MBR2GPT command, your disk partition must meet the requirements below. Otherwise, the conversion cannot be successful. But do not worry; before any changes to the disk are made, MBR2GPT validates the layout and geometry of the selected disk. If any of these checks fail, the conversion will not proceed, and an error message will be returned. Your disk partitions will not be damaged.
① Preconditions to Run the MBR2GPT Command in Server 2012 R2:
- There should be no Logical drive on this MBR disk.
- There should be a maximum of 3 Primary partitions on this MBR disk.
- One of the partitions is set as "Active" and is the system partition.
- All partitions on this MBR disk are supported by Windows, which means there are no EXT2/EXT3 or other types of Linux or Mac partitions.
② Common Issues and Corresponding Solutions
"Validating layout, disk sector size is: 512 bytes Disk layout validating failed for disk 0", "MBR2GPT: Conversion failed". This is the most common error message while converting MBR to GPT in Windows Server 2012 and other versions. If you receive such an error, check your disk partition configuration again.
On most Windows 2012 server system disks, there is a System Reserved partition, a C: drive (for the OS), and a D: drive. If all these partitions are Primary, you can convert the disk to GPT successfully. If your disk partition layout does not meet the requirements, follow the methods to modify it:
- If there is a Logical drive, convert it to Primary (without data loss).
- If there are 4 Primary partitions, follow the steps to move one to another disk.
- If there is a non-supported partition, you have to move the files and delete this partition.
③ Expand the System Reserved Partition (Optional)
For Windows to remain bootable after the conversion, an EFI system partition (ESP) must be in place. MBR2GPT will shrink the "System Reserved" partition at first. If there is not enough free space in this partition, MBR2GPT will shrink the C drive instead, and the EFI partition will be created behind the C drive after converting to a GPT disk.
When right-clicking the EFI partition in Disk Management, all options are grayed out. That means Disk Management cannot shrink, extend, or do any other operations to this partition. However, it does not matter to NIUBI Partition Editor, because it can shrink, extend, and move the EFI/Recovery partition without losing the files in it.
If you want to place the EFI partition on the left of the C drive, Download NIUBI Partition Editor and follow the method in the video to expand the System Reserved partition (it is enough to add 1 or 2GB):
④ How to Run MBR2GPT.exe in Server 2012 R2 to Convert a Disk with Command
As stated above, MBR2GPT.exe is built into Windows Server 2019 and Windows 10; it is not included in earlier Windows versions. To run MBR2GPT in Server 2012 R2, you need the Windows Preinstallation Environment and must run the command prompt from it.
Steps to convert MBR to GPT in Windows Server 2012 R2 with the MBR2GPT command:
Step 1: Download the Windows Server 2019 ISO and create a bootable DVD or USB flash drive with a Windows built-in or third-party tool. If you use a VMware or Hyper-V virtual machine, you just need to select this ISO file and boot from it.
Step 2: Boot from this bootable media, simply click Next in the first Windows Setup window, then click "Repair your computer" on the bottom left corner of the next window.
Step 3: Click "Troubleshoot" in the next window, then click Command Prompt.
Step 4: Just input 2 commands to complete the conversion:
- cd..
- mbr2gpt /convert
As you can see, the command window reports that the conversion completed successfully.
If the System Reserved partition was extended in advance, after restarting the server and booting into UEFI, Disk 0 is converted to GPT, and the EFI partition is created on the left side of the C drive.
Besides shrinking, extending partitions, and converting MBR to GPT in Server 2012/2016/2019/2022/2025, NIUBI Partition Editor helps you convert partitions between Primary and Logical, and convert NTFS to FAT32 without losing data. It also helps you move, merge, clone, wipe partitions, and much more.
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